A method for enhancing in-situ oxidation of persulfate to remove petroleum hydrocarbons from soil

Abstract

This invention relates to a method for enhancing in-situ oxidation of persulfate to remove petroleum hydrocarbons from soil, belonging to the field of soil remediation technology. The method for removing petroleum hydrocarbons from soil according to this invention includes the following steps: a) adding 3-6% (by weight of the soil) of sodium persulfate to the contaminated soil, mixing thoroughly, and reacting until the sodium persulfate content in the soil decreases to 40-60%; b) continuing to add hydroxylamine hydrochloride, the amount of hydroxylamine added being 2.4-3.6% of the mass of sodium persulfate added in step a; c) reacting until the sodium persulfate content in the soil decreases to 5-15%. Compared with existing methods, this method for removing petroleum hydrocarbons from soil has lower soil remediation costs and significantly better results.

Description

Technical Field

[0001] This invention relates to a method for enhancing the in-situ oxidation of persulfate to remove petroleum hydrocarbons from soil, belonging to the field of soil remediation technology. Background Technology

[0002] In-situ chemical oxidation (ISCO) is a crucial method for the remediation of petroleum-contaminated soil. ISCO involves injecting strong oxidants into contaminated soil to oxidize and degrade organic pollutants, reducing their quantity or toxicity and making them more readily utilized and degraded by microorganisms. Sodium persulfate (Na₂S₂O₈, PDS), as an oxidant, maintains an effective concentration and wide diffusion range in soil for a relatively long time, making it a key oxidant used in ISCO for removing organic pollutants from soil.

[0003] In soil organic pollution, the binding modes of organic pollutants and soil particles differ, mainly including the adsorption of organic pollutants by soil particles and the strong binding of organic pollutants by soil organic matter through dissolution and partitioning. In petroleum-contaminated soils, because petroleum hydrocarbons are often hydrophobic, they are mostly adsorbed onto the surface of soil particles or dissolved in soil organic matter, thus binding tightly to the soil particles. Traditional ISCO requires a solution system as a medium to promote the mass transfer and diffusion process of oxidants and activators, forming a homogeneous and heterogeneous mixed system. The activation process of PDS by added activators (such as ferrous salts or strong bases) mostly occurs in the liquid phase system, generating SO4. ·- Due to its extremely short half-life (~40 μs), it is difficult for oxidants to effectively contact organic pollutants adsorbed on the surface of soil particles or dissolved in soil organic matter, which reduces the removal efficiency of pollutants by oxidants. Often, a large amount of oxidants and activators are required to achieve a certain pollutant removal rate.

[0004] Patent application CN115338245A discloses a method for efficiently removing organic matter from soil using sodium persulfate. In this application, 5% by weight of soil blank, iron powder, ferric chloride, ferric oxide, ferrous sulfate, and composite material were used as catalysts, and 5% by weight of PDS was added to each. After 24 hours of reaction, the removal rates of TPH were 43.3%, 66.5%, 60.2%, 55.2%, 71.8%, and 85.7%, respectively. However, the preparation process of the composite material is complex and the cost is high.

[0005] Patent application CN115368905A discloses a composition with the function of degrading organic pollutants and its application. The composition includes a solid peroxide, a ferrous complex, and a free-standing persulfate, wherein the mass ratio of the persulfate to the solid peroxide is 1:1-5, and the composition does not contain a surfactant. This invention also provides a method for remediating contaminated soil, comprising the following steps: (1) mixing the solid peroxide, the ferrous complex, and the contaminated soil in the presence of a solvent; (2) mixing the product obtained from the first mixture with the persulfate in a second mixture; wherein the time for the first mixture accounts for 1 / 5-4 / 5 of the sum of the times for the first and second mixtures. This invention improves the degradation rate of soil organic pollutants (especially polycyclic aromatic hydrocarbons) to a certain extent and reduces the degradation time. However, this method requires first mixing the solid peroxide, the ferrous complex, and the contaminated soil in the presence of a solvent, followed by centrifugation to separate the product and then mixing it with the persulfate in a second reaction. This method is costly and its application is currently limited to the laboratory stage. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a new method for removing petroleum hydrocarbons from soil.

[0007] The method for removing petroleum hydrocarbons from soil according to the present invention includes the following steps:

[0008] a. Add 1-6% of sodium persulfate by soil mass to the contaminated soil, mix well, and react until the sodium persulfate content in the soil is reduced to 40-60%.

[0009] b. Continue adding hydroxylamine hydrochloride, the amount of hydroxylamine added is 2.4-3.6% of the mass of sodium persulfate added in step a;

[0010] c. The reaction reduces the sodium persulfate content in the soil to 5-15%.

[0011] In step a above, it is preferable to add 5% sodium persulfate by weight of the soil to the contaminated soil.

[0012] In step a above, it is preferable that the reaction proceeds until the sodium persulfate content in the soil is reduced to 40-50%.

[0013] Furthermore, the amount of hydroxylamine hydrochloride added in step b above can be adjusted appropriately according to the Fe and Mn content in the soil. If the Fe and Mn content in the soil is high, the amount of hydroxylamine hydrochloride added can be reduced appropriately; if the Fe and Mn content is low, the amount of hydroxylamine hydrochloride added can be increased appropriately. Generally, the amount of hydroxylamine hydrochloride added in step b is 2.8-3.2% of the mass of sodium persulfate added in step a, and preferably 3% of the mass of sodium persulfate added in step a.

[0014] In step c above, it is preferable that the reaction proceeds until the sodium persulfate content in the soil is reduced to 5-10%.

[0015] Furthermore, in the method for removing petroleum hydrocarbons from soil according to the present invention, sodium persulfate is added to the contaminated soil, mixed thoroughly, and reacted for 48-100 hours, followed by the addition of hydroxylamine hydrochloride. More preferably, sodium persulfate is added to the contaminated soil, mixed thoroughly, and reacted for 90-98 hours, followed by the addition of hydroxylamine hydrochloride.

[0016] In the method for removing petroleum hydrocarbons from soil according to the present invention, after adding hydroxylamine hydrochloride, the reaction is continued for 120-150 hours.

[0017] Furthermore, in the method for removing petroleum hydrocarbons from soil according to the present invention, after adding hydroxylamine hydrochloride, it is preferable to continue the reaction for another 140-150 hours.

[0018] The present invention relates to a method for removing petroleum hydrocarbons from soil. This method utilizes the iron and manganese minerals in the soil particles to activate PDS, resulting in a catalytic activation reaction on the surface of the soil particles. The generated sulfate free radicals can more effectively react with petroleum hydrocarbons adsorbed on the surface of the soil particles. After a period of reaction, the reducing agent hydroxylamine hydrochloride is added, which reduces the oxidized iron and manganese on the surface of the soil particles to a lower valence reduced state, which can further activate PDS. The total petroleum hydrocarbon removal rate can reach more than 85% when the PDS dosage is 5%. Compared with existing methods, this method has lower soil remediation costs and significant effects. Attached Figure Description

[0019] Figure 1 The graph shows the changes in total petroleum hydrocarbon (TPH) concentration.

[0020] Figure 2 This is a graph showing the change in the remaining concentration of the oxidant PDS. Detailed Implementation

[0021] The method for removing petroleum hydrocarbons from soil according to the present invention includes the following steps:

[0022] a. Add 1-6% of sodium persulfate by soil mass to the contaminated soil, mix well, and react until the sodium persulfate content in the soil is reduced to 40-60%.

[0023] b. Continue adding hydroxylamine hydrochloride, the amount of hydroxylamine added is 2.4-3.6% of the mass of sodium persulfate added in step a;

[0024] c. The reaction reduces the sodium persulfate content in the soil to 5-15%.

[0025] In one specific embodiment, in step a above, 1% sodium persulfate by soil mass can be added; in another specific embodiment, 2% sodium persulfate by soil mass can be added; in another specific embodiment, 3% sodium persulfate by soil mass can be added; in another specific embodiment, 4% sodium persulfate by soil mass can be added; in another specific embodiment, 5% sodium persulfate by soil mass can be added; and in another specific embodiment, 6% sodium persulfate by soil mass can be added. Furthermore, to improve the removal efficiency of petroleum hydrocarbons from the soil, it is preferable to add 5% sodium persulfate by soil mass to the contaminated soil.

[0026] In step a above, it is preferable that the reaction proceeds until the sodium persulfate content in the soil is reduced to 40-50%.

[0027] Furthermore, the amount of hydroxylamine hydrochloride added in step b above can be adjusted appropriately according to the Fe and Mn content in the soil. If the Fe and Mn content in the soil is high, the amount of hydroxylamine hydrochloride added can be appropriately reduced; if the Fe and Mn content is low, the amount of hydroxylamine hydrochloride added can be appropriately increased. The amount of hydroxylamine hydrochloride added in step b can be 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, or 3.6% of the mass of sodium persulfate added in step a. Generally, the amount of hydroxylamine hydrochloride added in step b is 2.8-3.2% of the mass of sodium persulfate added in step a, and preferably 3% of the mass of sodium persulfate added in step a.

[0028] In step c above, it is preferable that the reaction proceeds until the sodium persulfate content in the soil is reduced to 5-10%.

[0029] Furthermore, in the method for removing petroleum hydrocarbons from soil according to the present invention, sodium persulfate is added to the contaminated soil, mixed thoroughly, and reacted for 48-100 hours, followed by the addition of hydroxylamine hydrochloride. More preferably, sodium persulfate is added to the contaminated soil, mixed thoroughly, and reacted for 90-98 hours, followed by the addition of hydroxylamine hydrochloride.

[0030] In the method for removing petroleum hydrocarbons from soil according to the present invention, after adding hydroxylamine hydrochloride, the reaction is continued for 120-150 hours.

[0031] Furthermore, in the method for removing petroleum hydrocarbons from soil according to the present invention, after adding hydroxylamine hydrochloride, it is preferable to continue the reaction for another 140-150 hours.

[0032] The specific embodiments of the present invention will be further described below with reference to examples, but the present invention is not limited to the scope of the embodiments described herein.

[0033] The soil test results for the petroleum hydrocarbon-contaminated oil-stained soil used in the following examples and comparative examples are as follows:

[0034] Soil iron and manganese mineral content: available iron 2.76 × 10⁻⁶ 3 (mg·kg -1 Available manganese 10.2 (mg·kg) -1 )

[0035] Soil organic matter content: 26.5 g / kg -1 ).

[0036] Soil texture (particle size distribution): Soil bulk density 1.51 g·cm³ -3 Soil density 2.5 g·cm³ -3 Soil porosity was 39.5%, particle size > 2 mm accounted for 5.63%, particle size 2-0.02 mm accounted for 53.21%, particle size 0.02-0.002 mm accounted for 22.97%, and particle size < 0.002 mm accounted for 18.19%.

[0037] Petroleum hydrocarbon content: 4987.865 mg / kg.

[0038] Example 1

[0039] In oil-contaminated soil polluted with petroleum hydrocarbons, PDS was added at a rate of 1% (by mass of the contaminated soil). After 4 days of reaction, hydroxylamine hydrochloride at a rate of 3% of the PDS mass was added. After another 6 days of reaction, the treatment with added hydroxylamine hydrochloride showed a significantly higher total petroleum hydrocarbon removal rate than the control group without added hydroxylamine, increasing by 15.7%.

[0040] Example 2

[0041] In oil-contaminated soil polluted with petroleum hydrocarbons, PDS was added at a rate of 3% (by mass of the contaminated soil). After 4 days of reaction, hydroxylamine hydrochloride at a rate of 3% of the PDS mass was added. After another 6 days of reaction, the treatment with added hydroxylamine hydrochloride showed a significantly higher total petroleum hydrocarbon removal rate than the control group without added hydroxylamine, increasing by 16.1%.

[0042] Example 3

[0043] In oil-contaminated soil polluted with petroleum hydrocarbons, PDS was added at a dosage of 5% (by mass of the contaminated soil). After 4 days of reaction, hydroxylamine hydrochloride at a dosage of 3% of the PDS mass was added. After 6 more days of reaction, the treatment with added hydroxylamine hydrochloride showed a significantly higher total petroleum hydrocarbon removal rate than the control group without added hydroxylamine, increasing by 37.4%. The highest total petroleum hydrocarbon removal rate, reaching 85.4%, was achieved in the treatment with 5% PDS. Figure 1 (As shown).

[0044] Comparative Example 1

[0045] In petroleum hydrocarbon-contaminated soil, PDS was added at a rate of 1% (by mass of the contaminated soil). On day 0 (the start of the reaction), hydroxylamine hydrochloride at a mass of 3% of the PDS was added. Results showed that PDS rapidly decomposed during the first four days of the reaction. Figure 2 However, the total petroleum hydrocarbon removal was actually lower than that of the control group. Compared with the control group without hydroxylamine hydrochloride, in the treatment where hydroxylamine hydrochloride was added simultaneously with PDS on day 0 of the reaction, the total petroleum hydrocarbon removal rate was 34.5% lower after 4 days of reaction and 17.3% lower after 10 days of reaction.

[0046] Comparative Example 2

[0047] In petroleum hydrocarbon-contaminated soil, PDS was added at a rate of 3% (by mass of the contaminated soil). On day 0 of the reaction (i.e., at the start of the reaction), hydroxylamine hydrochloride at a mass of 3% of the PDS was added. The results showed that PDS rapidly decomposed during the first four days of the reaction. Figure 2 However, the total petroleum hydrocarbon removal was actually lower than that of the control group. Compared with the control group without hydroxylamine hydrochloride, in the treatment where hydroxylamine hydrochloride was added simultaneously with PDS on day 0 of the reaction, the total petroleum hydrocarbon removal rate was 32.0% lower after 4 days of reaction and 18.8% lower after 10 days of reaction.

[0048] Comparative Example 3

[0049] In petroleum hydrocarbon-contaminated soil, PDS was added at a rate of 5% (by mass of the contaminated soil). On day 0 (the start of the reaction), hydroxylamine hydrochloride at a mass of 3% of the PDS was added. The results showed that PDS rapidly decomposed during the first four days of the reaction. Figure 2 However, the total petroleum hydrocarbon removal was actually lower than that of the control group. Compared with the control group without hydroxylamine hydrochloride, in the treatment where hydroxylamine hydrochloride was added simultaneously with PDS on day 0 of the reaction, the total petroleum hydrocarbon removal rate was 34.6% lower after 4 days of reaction and 0% lower after 10 days of reaction.

[0050] As can be seen from the examples and comparative examples, adding PDS first and reacting for a period of time, followed by the addition of hydroxylamine hydrochloride, can significantly improve the total petroleum hydrocarbon removal rate.

Claims

1. A method for removing petroleum hydrocarbons from soil, characterized in that, Includes the following steps: a. Add 1-6% sodium persulfate by weight to the petroleum hydrocarbon contaminated soil, mix well, and utilize the iron and manganese minerals in the soil particles to activate the sodium persulfate until the sodium persulfate content in the soil is reduced to 40-60%. b. Continue adding hydroxylamine hydrochloride, the amount of which is 2.4-3.6% of the mass of sodium persulfate added in step a; the amount of hydroxylamine hydrochloride added in step b should be adjusted according to the Fe and Mn content in the soil; if the Fe and Mn content in the soil is too high, reduce the amount of hydroxylamine hydrochloride added; if the Fe and Mn content is too low, increase the amount of hydroxylamine hydrochloride added. c. The reaction reduces the sodium persulfate content in the soil to 5-15%.

2. The method of removing soil petroleum hydrocarbons according to claim 1, wherein: In step a, sodium persulfate is added to the contaminated soil at a concentration of 5% of the soil mass.

3. The method of removing soil petroleum hydrocarbons of claim 1, wherein: In step a, the reaction proceeds until the sodium persulfate content in the soil decreases to 40-50%.

4. The method of removing soil petroleum hydrocarbons of claim 1, wherein: In step b, the amount of hydroxylamine hydrochloride added is 2.8-3.2% of the mass of sodium persulfate added in step a.

5. The method for removing petroleum hydrocarbons from soil according to claim 1, characterized in that: In step b, the amount of hydroxylamine hydrochloride added is 3% of the mass of sodium persulfate added in step a.

6. The method for removing petroleum hydrocarbons from soil according to claim 1, characterized in that: In step c, the reaction continues until the sodium persulfate content in the soil decreases to 5-10%.

7. The method for removing petroleum hydrocarbons from soil according to claim 1, characterized in that: Sodium persulfate was added to the contaminated soil and mixed thoroughly. The mixture was allowed to react for 48-100 hours, and then hydroxylamine hydrochloride was added.

8. The method for removing petroleum hydrocarbons from soil according to claim 4, characterized in that: Sodium persulfate was added to the contaminated soil and mixed thoroughly. The mixture was allowed to react for 90-98 hours, and then hydroxylamine hydrochloride was added.

9. The method for removing petroleum hydrocarbons from soil according to claim 6 or 7, characterized in that: After adding hydroxylamine hydrochloride, continue the reaction for another 120-150 hours.

10. The method for removing petroleum hydrocarbons from soil according to claim 6 or 7, characterized in that: After adding hydroxylamine hydrochloride, continue the reaction for another 140-150 hours.

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